The conventional type of filter element is made from a tape like material to which synthetic resin is permeated. After the material is bent to a serpentine form, the wavy material is rounded and connected at both ends to form a ring. The material is then supported by a supporting member which is provided at an inner side of the ring shaped material. Finally, the shape of the material is fixed by hardening the resin.
The filter element having the shape shown in FIG. 21 may be used as an air filter for an automotive engine. However, the so called "crystal type" filter element similar to the filter shown in FIG. 22, has become a more popular automotive air filter design instead of the filter design shown in FIG. 21, since the crystal type filter works more effectively.
The crystal type filter element has a plurality of wavy portions with the width of the wavy portions gradually varied. The sets of wavy portions thus create filtering cores which are arranged circularly so that a group of filtering cores make a ring.
Since the crystal type filter element has such a complicated shape, which is not easily produced, a method and apparatus for automatically forming the crystal type filter element is needed.